1. Field of the Invention
This invention relates to a new process for the purification of methacrylamidopropyltrimethylammonium chloride (MAPTAC) or of the free amine, dimethylaminopropylmethacrylamide (DMAPMA), through the application of adsorption techniques. The invention more particularly relates to the purification, by both batch and continuous processing, of aqueous solutions of MAPTAC or DMAPMA by passing such solutions over a bed of solid, nonionic organic resin or by stirring such solutions with the resin in a batch treatment tank.
2. Description of the Prior Art
Methacrylamidopropyltrimethylammonium chloride, among its other uses, is an important monomer in the synthesis of a class of water soluble cationic polymers which find application as flocculants and as retention aids in the production of paper as taught by U.S. Pat. No. 3,661,880.
Aqueous solutions of commercially available MAPTAC or the free amine vary in color from light yellow to dark amber. This color, or impurity, is carried through upon polymerization of the monomer resulting in polymer products of low molecular weight and widely varying color. Widespread variations in product color or impurities result in polymers having unacceptable performance characteristics. Further, the impurity in the monomer also may cause other undesirable polymer variations such as variations in clarity and viscosity.
While the impurities may be removed effectively from the free amine by vacuum distillation techniques leading to a preferential distillate which is clear and "water white" and which, upon subsequent polymerization, led to a clear and "water white" polymer product, such vacuum distillation techniques do not lend themselves readily to continuous processing and are prohibitively expensive as a commercial process. In addition, the amine is easily activated in this form and may polymerize at distillation temperature, creating additional and undesirable processing problems.
The impurities may also be effectively removed by treatment with activated carbon as described in U.S. Pat. No. 3,907,891. However, as will be shown, the activated carbon treatment will remove the polymerization inhibitor, such as the methylether of hydroquinone (MEHQ), as well as the impurities. Therefore, there remains a need for a method which will remove the impurities from MAPTAC and DMAPMA but which will not appreciably eliminate the presence of any polymerization inhibitor. It is important to have a certain level of polymerization inhibitor in MAPTAC to prevent premature polymerization while the MAPTAC is being stored or shipped.
The method of this invention uses solid, nonionic organic resins as means to remove the organic impurities. One kind of resin, used in the experiments described herein, is the AMBERLITE.RTM. XAD series of resins manufactured by Rohm and Haas Company. The Rohm and Haas technical bulletins describe the various uses of the AMBERLITE XAD resins which include water purification, phenol removal, and pesticide and narcotic detection.